Maritime chemical tanker having composite tanks for storing and/or transporting liquid organic and inorganic chemicals and the like

BACKGROUND OF THE INVENTION

The present invention relates to the composite tank arts. It finds particular application in conjunction with maritime chemical tankers having composite storage tanks for use in transporting and storing liquid organic and inorganic chemicals, and will be described with particular reference thereto. The present invention also finds application in conjunction with composite iso-tank containers for use in transporting and storing liquid organic and inorganic chemicals on maritime container ships, railroad cars, and roadway semi-trailers.

Seaborne trade in liquid organic and inorganic chemicals has grown tremendously over the past decade. This growth is accompanied with the ever present dangers of massive ecological damage should any of the present tanker ships have a chemical spill due to collision with another ship or ship breakup due to internal corrosion and/or rough seas.

With the growing demand for the transportation of hazardous chemicals by sea, new designs, safety equipment, and containment procedures have been developed. One such design is full, double-hulled ships with the port and starboard wings being used to carry less hazardous cargoes. Further, due to the inability of present coatings to resist the corrosive effects of the more aggressive cargoes, more and more chemical tanker's cargo tanks are being built of stainless steel. However, the cost for the stainless steel tanks can, on larger chemical tankers, cost as much as the rest of the ship, including the steel hull, engine room equipment and outfitting.

A major problem facing maritime chemical tanker operators and owners is the time spent in port which remains very long in relation to time spent at sea. Chemical tanker owners and operators face a port time of their entire fleet of deep-sea tankers of around 40%. This causes a tremendous loss in charter revenue. This port time is, in part, due to the requirement of washing and cleaning the cargo tanks prior to loading the next cargo. With present tanker designs, which incorporate integral rectangular stainless steel cargo tanks, large hard to reach surfaces have to be washed down with chemicals to remove the residue of the previous cargo. This takes an excessive amount of time plus it produces large quantities of hazardous waste water, typically referred to as “slops”. Slops have to be treated and neutralized before being pumped overboard, or have to be pumped ashore for treatment. In either case, washing known rectangular stainless steel cargo tanks is a very costly and time consuming process.

It has been proposed to build cylindrical stainless steel tanks which are easier to clean. The use of cylindrical stainless steel cargo tanks reduces the amount of slops required to clean the cargo tanks, reduces the time spent in port cleaning the tanks, and reduces the costs associated with neutralizing the slops that are produced. However, it is more expensive to manufacturer cylindrical stainless steel cargo tanks. Thus, the use of cylindrical stainless steel cargo tanks increases the manufacturing cost of the ship, reduces carrying capacity of the cargo tanks due to loss of area of a cylinder versus that of a rectangle, and increases the weight and length of the ship in order to carry the same volume of cargo as a ship having rectangular cargo tanks.

Also, the transportation of liquid organic and inorganic chemicals by rail and over-the-road presents numerous hazards to humans, animals, and the environment.

Accordingly, it has been considered desirable to develop a new and improved composite storage tank for transporting and storing liquid organic and inorganic chemicals, which meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a maritime vessel is disclosed. The maritime vessel includes a hull and at least one cargo tank associated with the hull and having a multi-layered side wall construction. The side wall construction includes a first layer providing a corrosion barrier for the cargo tank, a second layer providing structural integrity for the cargo tank, a third layer providing impact energy absorption and buoyancy properties for the cargo tank, and a fourth layer providing fire-resistant properties for the cargo tank.

In accordance with another aspect of the present invention, an iso-tank is disclosed. The iso-tank has a multi-layer sidewall construction including a first layer providing a corrosion barrier for the iso-tank, a second layer providing structural integrity for the iso-tank, a third layer providing impact energy absorption and buoyancy properties for the iso-tank, a fourth layer providing fire-resistant properties for the iso-tank, and a protective super-structure surrounding the iso-tank.

One advantage of the present invention is the provision of a lighter tonnage chemical tanker which incorporates multi-layer composite cargo tanks.

Another advantage of the present invention is the provision of a faster chemical tanker which can carry more cargo at the same draft in a smaller ship relative to stainless steel tank ships.

Yet another advantage of the present invention is the provision of a chemical tanker having 50% less shore time than stainless steel tank ships.

Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiments) and are not to be construed as limiting the invention.

FIG. 1

is a side elevation view of an exemplary maritime chemical tanker which incorporates one or more composite storage tanks in accordance with a first embodiment of the present invention;

FIG. 2

is a longitudinal cross-section view of the chemical tanker of

FIG. 1

taken along the line

2

—

2

in

FIG. 3

;

FIG. 3

is a top view of the chemical tanker of

FIG. 1

;

FIG. 4

is a cross-section view of the chemical tanker of

FIG. 1

taken along the line

4

—

4

of

FIG. 3

;

FIG. 5

is a cut-way view of a composite storage tank in accordance with the first embodiment of the present invention;

FIG. 6

is an enlarged perspective view of a sump region of the composite storage tank of

FIG. 5

;

FIG. 7

is an enlarged cross-section view of a side wall of the composite storage tank of

FIG. 5

;

FIG. 8

is a side elevation view of composite storage tank in accordance with a second embodiment of the present invention;

FIG. 9

is an enlarged cross-section view of a side wall of the composite storage tank of

FIG. 8

; and

FIG. 10

is a chart showing the performance characteristics of different honeycomb sandwich sidewall constructions each having a different thickness of honeycomb and/or high-density foam layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT (S)

With reference now to FIGS.

1

-

4

, an exemplary maritime chemical tanker

10

includes a hull

12

having at least one or more composite storage tanks

14

therein.

FIG. 3

illustrates an exemplary layout for the composite storage tanks

14

within the hull

12

of the chemical tanker

10

. The composite storage tanks

14

have a substantially cylindrical shape, and have various capacity ratings for storing corrosive and non-corrosive liquid organic and inorganic chemicals such as crude oil, liquid natural gas (LNG), liquid propane gas (LPG), etc. Liquid organic and inorganic chemicals may be pumped into and out of the composite storage tanks

14

through a distribution manifold

16

and supply pipes

18

proximate a deck

20

of the chemical tanker

10

.

In the embodiment being described, the volume of each of the composite storage tanks T

1

is approximately 574 cubic meters (M

3

); the volume of each of the composite storage tanks T

2

is approximately 500 cubic meters (M

3

); the volume of each of the composite storage tanks T

3

is approximately 400 cubic meters (M

3

); the volume of each of the composite storage tanks T

4

is approximately 380 cubic meters (M

3

) ; the volume of each of the composite storage tanks T

5

is approximately 367 cubic meters (M

3

); and the volume of each of the composite storage tanks T

6

is approximately 241 cubic meters (M

3

). As a result, the chemical tanker

10

may have a total cargo capacity of approximately 13,432.5 cubic meters (M

3

).

The composite storage tanks

14

are separately secured to the hull

12

of the chemical tanker

10

by any suitable manner known in the art. Thus, the composite tanks are independent and not part of the chemical tanker's structure, thereby reducing the potential damage to the tanks

14

in the event the chemical tanker is ever damaged. Further, the tanks

14

can be removed and reused on a new tanker after the original tanker has reached its useful life.

Referring now to

FIGS. 5 and 6

, an exemplary composite storage tank

14

in accordance with a first embodiment of the present invention is shown. The composite storage tank

14

includes an integral upper dome portion

22

, an upright cylindrical side wall portion

24

, and a lower dome portion

26

which cooperate to define an interior cavity or chamber

28

. A neck portion

30

extends from the upper dome

22

to define an opening or manway

32

into the tank

14

. An annular flange

34

extends around an upper extent of the neck portion

30

to provide a sealing surface for receiving a lid or cap

36

. A sump

38

is defined in the lowest extent of the lower dome

26

. A skirt

40

extends from an exterior surface of the lower dome

26

to support the composite tank

14

within the hull

12

of the chemical tanker

10

.

A main suction pipe

42

extends through the opening

32

into the chamber

28

. A suction bell

44

extends from a lower free end of the main suction pipe

42

. The suction bell

44

is positioned within the sump

38

to convey liquids stored in the tank

14

up through the main suction pipe

42

and out through the opening

32

to the manifold

16

. At least one, and preferably two stripper pipes

46

extend from the opening

32

along the main suction pipe

42

into the suction bell

44

within the sump

38

. The stripper pipes

46

convey slops that accumulate in the sump

38

during washing and cleaning of the tank

14

out through the opening

32

. A ladder

48

can extend from the opening

32

along the main suction pipe

42

and stripper pipes

46

to the lower dome

26

. One or more work platforms

50

may be positioned along the ladder

48

to permit a worker to enter into the tank during cleaning and/or inspection procedures. The ladder

48

and platforms)

50

can be formed from composite materials or inert materials to prevent chemical reactions with liquid chemicals that are stored and/or transported within the tank

14

. Liquids can be pumped out of the tank in any manner known in the art. For instance, an inert gas such as nitrogen (N

2

) can be pumped into the tank

14

through a supply pipe

51

to provide a blanket pressure of approximately 0.5 atmospheres to push the liquid out of the tank.

Referring now to

FIG. 7

, there is shown a cross-section of a multi-layered side wall

52

defining the composite storage tank

14

. The side wall

52

includes a first or innermost corrosion barrier or corrosion-resistant layer

54

. The corrosion barrier

54

is formed from at least a resin material such as organic/inorganic polymers, flouro polymers, etc., and reinforcement material such as carbon fibers, Teflon, polyester, etc., in the form of at least one thin sheet or veil which holds the resin material in place. In the preferred embodiment, the resin material is an organic/inorganic polymer such as a siloxirane and the reinforcement material is carbon fibers. It should be appreciated that carbon fibers reinforcement material facilitates discharging static electricity that builds up or is generated on the inner surface of the tank

14

due to fluid flow within the tank.

The thickness of the corrosion barrier

54

depends upon the particular capacity rating of the tank

14

. For instance, the thickness of the corrosion barrier

54

for the larger cargo tanks T

1

is in the range of about 0.060 to about 0.130 inches, and preferably about 0.100 inches, including about three layers or windings of reinforcement material. The thickness of the corrosion barrier

54

for the smaller cargo tanks T

6

is in the range of about 0.048 to about 0.130 inches, and preferably about 0.0100 inches, including about three layers or windings of reinforcement material.

Alternatively, the corrosion barrier

54

could include a low surface energy fluorinated thermoplastic thin sheet liner such as a 5 to 10 mil (0.005 to 0.010 inches) thick polyvinylidene fluoride (PVDF) film which has a low permeability rate and is corrosion resistant to most chemicals. The low surface energy of PVDF is approximately 20 to 23 dynes per centimeter compared to stainless steel which is over 300 dynes per centimeter.

The low surface energy of PVDF or other fluorinated thermoplastics prevents cargoes from sticking to the inner side wall of the tank thereby allowing most liquids to drain to the bottom of the tank for easy pumping. Thus, only a small amount of hot water is required to clean the tanks for the next cargo. This reduces port time and the amount of slops generated. It is contemplated that a composite tank with a fluoropolymer liner can be cleaned in about 5 to 8 minutes, which represents a time savings of approximately 90% over the time required to clean a comparably sized stainless steel tank. The reduction of hazardous waste water or slops is also approximately 90%.

An inner wall

56

surrounds the corrosion barrier

54

. The inner wall

56

is formed from at least a resin material such as organic/inorganic polymers, flouro polymers, etc., and a reinforcement material such as fiberglass, aramid carbon fibers, graphite fibers, organic fibers, etc. The inner wall

56

provides structural integrity to the tank

14

. In the preferred embodiment, the resin material is an organic/inorganic polymer such as a siloxirane and the reinforcement material is fiberglass.

The thickness of the inner wall

56

depends upon the particular capacity rating of the tank

14

. For instance, the thickness of the inner wall

56

for the larger cargo tanks Ti is in the range of about 0.125 to about 0.300 inches, and preferably about 0.250 inches, including about eight layers or windings of reinforcement material. The thickness of the inner wall

56

for the smaller cargo tanks T

6

is in the range of about 0.100 to about 0.200 inches, and preferably about 0.150 inches, including about six layers or windings of reinforcement material.

A third layer

58

surrounds the inner wall

56

. The third layer

58

can be formed from a honeycomb material, a high-density foam material, or a combination of honeycomb and high-density foam materials, etc. As shown in

FIG. 10

, the use of honeycomb and/or high-density foam materials for the third layer

58

results in a sandwiched sidewall construction that provides high strength with light weight. Further, the third layer

58

absorbs energy at a constant rate. The energy absorption is due to the loading increasing up to a peak value (bare compressive strength) before starting to crush at a uniform load (about 50% of the peak load) until it bottoms out (can no longer crush).

Thus, energy absorption property of the third layer

58

protects against spillage in the event that the chemical tanker

10

were to be hit by another ship or run aground. The third layer

58

not only provides structural integrity to the tank

14

, but it also adds a buoyancy factor to the tank

14

that permits the tank

14

to float, even when full, should the chemical tanker

10

ever sink.

The composite storage tanks

14

may be secured to the hull

12

with shear pins or bolts

61

(

FIG. 5

) which permit the tanks

14

to break loose from the deck

20

in the event of high impact. This permits the tanks

14

to react like bowling pins and stack up against one another to cushion the load. The tanks

14

become oval or elliptical when a sufficient external load is present. This ellipticalization, along with the inherent energy absorption characteristics of the third layer

58

, makes the composite cargo tanks

14

almost unbreakable. Further, the shear bolts permit the cargo tanks

14

to separate from the deck

20

and float free of the hull

12

, thus preventing spillage in the event that the chemical tanker were to sink due to catastrophic damage.

In the preferred embodiment, the third layer

58

is formed from a rigid phenolic foam material having a density of approximately 6-9 lbs/sq. ft. The thickness of the layer

58

depends upon the particular capacity and buoyancy ratings of the tank

14

. For instance, the thickness of the layer

58

for the larger cargo tanks T

1

is in the range of about 1.00 to about 3.00 inches, and preferably about 1.50 inches. The thickness of the layer

58

for the smaller cargo tanks T

6

is in the range of about 0.25 to about 2.00 inches, and preferably about 0.38 inches.

An outer wall

60

surrounds the third layer

58

. The outer wall

60

is formed from at least a resin material such as organic/inorganic polymers, flouro polymers, etc., and a reinforcement material such as fiberglass, aramid carbon fibers, graphite fibers, organic fibers, etc. In the preferred embodiment, the resin material is a phenolic resin and the reinforcement material is fiberglass. The use of phenolic resin in the outer wall

56

not only provides additional structural integrity to the tank

14

, but it also provides a fire resistance property to the tank

14

.

Fire protection of double wall (inner wall

56

and outer wall

60

) composite tanks can also be obtained by a number of other means, such as, but not limited to; 1) intumescent coatings which produce a ceramic-like insulating char at rapid temperature rises up to 2000° F. in five minutes, 2) fire retardant matrixes, 3) inorganic topcoat composites with steel mesh to dissipate localized heat or other such means, etc.

It should be appreciated that a potential fire hazard exists with single wall composite tank constructions because a single composite wall primarily provides structural integrity for a tank, as opposed to providing fire resistance. It should also be appreciated that a single wall composite tank construction is typically heavier than a comparably sized multi-wall composite tank construction because it does not include a high strength-to-weight ratio layer of honeycomb and/or high-density foam material like the third layer

58

.

The thickness of the outer wall

60

depends upon the particular capacity and fire resistance ratings of the tank

14

. For instance, the thickness of the outer wall

60

for the larger cargo tanks T

1

is in the range of about 0.100 to about 0.300 inches, and preferably about 0.180 inches, including about nine layers or windings of reinforcement material. The thickness of the outer wall

60

for the smaller cargo tanks T

6

is in the range of about 0.075 to about 0.200 inches, and preferably about 0.125 inches, including about five layers or windings of reinforcement material.

A number of sensing or monitoring devices

62

such as stress gauges, load cells, liquid level gauges, temperature gauges, thermal couples, etc., can be embedded between any of the multiple layers that form the side walls

52

of the storage tank

14

, preferably during manufacture, to monitor various tank and/or liquid cargo parameters. In the embodiment being described, the sensing devices

62

are mounted between the inner wall

56

and the third layer

58

. The sensing devices can be coupled to shipboard monitoring equipment (not shown) by wires and/or by telemetry antennas.

By incorporating stress gauges or load cells into the side wall of the lower dome portion

26

, the actual amount of cargo in the tank can be accurately monitored. That is, by knowing the empty weight of the composite storage tank, the loaded weight of the composite storage tank, and the specific gravity of the cargo in the composite storage tank, the actual amount of cargo can be determined in a known manner.

In contrast, a known method of determining the amount of cargo in a maritime storage tank requires a very expensive and relatively inaccurate microwave sensing system which approximates the amount of cargo stored in a maritime tank by transmitting a microwave signal into the tank and measuring the elapsed time for the microwave signal to reflect off the surface of the cargo stored in the tank and return to the sensor.

Fiber optic wires can also be embedded within the side walls

52

of the storage tank

14

, to allow for lighting within the tank. Video analysis of the inside of the tank increases safety for ship personnel by eliminating the need for a person to enter into a tank that could contain poisonous gases.

As previously mentioned, to compensate for the lost cargo volume when using cylindrical stainless steel maritime tanks, compared to rectangular stainless-steel maritime tanks, the size (i.e. length and/or berth) of the chemical tanker must be increased. However, because the weight of cylindrical composite maritime tanks

14

are less than comparably-sized cylindrical stainless maritime tanks. By way of comparison, a composite tank T

1

in accordance with the present invention weighs approximately 25,000 lbs while a stainless steel tank of substantially equal capacity weighs approximately 110,000 lbs. It should be appreciated that the height of cylindrical composite maritime tanks

14

can be increased to compensate for lost cargo volume without increasing the size of the chemical tanker.

Thus, by using composite materials, cylindrical, oval, or other elliptically-shaped maritime storage tanks can be used to reduce the weight of a chemical tanker while permitting an increased carrying capacity. Further, the use of composite materials reduces the initial, operating and maintenance costs of a chemical tanker, in part because composite tanks cost less than stainless steel tanks, and a standard design high-speed container ship or bulk carrier hull can be used.

By utilizing a conventional double hull chemical tanker and the double wall, i.e., inner wall

56

and outer wall

60

, composite maritime storage tanks

14

of the present invention, a quadruple structure or hull is formed. A quadruple structure or hull provides twice the protection of a conventional chemical tanker incorporating stainless steel cargo tanks. Further, by building maritime chemical tankers with the double wall composite tanks

14

, the tanks

14

can be individually removed and replaced with other tanks designed to handle pressurized cargoes, low or high temperature cargoes, or to repair or upgrade existing tanks. Due to the double wall insulative qualities the tanks

14

, a tank with a hot cargo (100° C.) can be positioned next to a tank with a cold cargo (−28° C.). This cannot be achieved with present stainless steel tank vessels.

In sum, the use of composite double wall maritime storage tanks results in a lighter weight chemical tanker that can carry more cargo at same draft in a smaller ship, that can operate at a faster speed, that reduces port time by 50% over stainless steel tank ships, and that generates 90% less hazardous waste (slop).

Further, composite maritime storage tanks in accordance with the present invention can carry all International Maritime Organization (IMO) approved cargoes without corrosion. Unlike the composite storage tanks of the present invention, the exterior surfaces of stainless steel maritime tanks must be coated to resist salt water corrosion/penetration that causes chloride stress cracking of the stainless steel.

Referring now to

FIG. 8

, there is shown a composite storage or ISO tank

70

, in accordance with another embodiment of the present invention. The ISO tank

70

includes a horizontally-oriented cylindrical portion

72

and two domed-end portions

74

,

76

formed integrally with respective ends of the cylindrical portion

72

. A substantially rectangular frame or superstructure

78

surrounds the ISO tank

70

. The superstructure

78

protects the ISO tank

70

from damage, and permits the ISO tank

70

to be transported over land by semi-trailer, or by rail car. Further, the superstructure

78

permits multiple ISO tanks

70

to be stacked for transport on conventional maritime container ships.

A neck portion

80

extends upward from the cylindrical portion

72

to define an opening

82

into the ISO tank

70

. An annular flange

84

extends around an upper extent of the neck portion

80

to provide a sealing surface for receiving a lid or cap (not shown). It should be appreciated that the composite tank

70

has a much smaller cargo capacity than the maritime storage tanks

14

. In particular, the volume of the composite ISO tank

70

is approximately 50 cubic meters (M

3

). Because the ISO tank

70

is movable, it is desirable to increase the structural integrity of the side wall

86

relative to the composite maritime tanks

14

of FIG.

5

.

Referring now to

FIG. 9

, there is shown a cross-section view of the multi-layered side wall

86

defining the composite ISO tank

70

. As with the side wall

52

, the construction of the side wall

86

includes a first or innermost corrosion barrier

88

. The corrosion barrier

88

is formed from at least a resin material such as organic/inorganic polymers, flouro polymers, etc., and reinforcement material such as carbon fibers, Teflon, polyester, etc., in the form of at least one thin sheet or veil which holds the resin material in place. In the preferred embodiment, the resin material is an organic/inorganic polymer such as a siloxirane and the reinforcement material is carbon fibers. It should be appreciated that carbon fibers reinforcement material facilitates discharging static electricity generated or built up within the inner surface of the tank

70

due to the flow of fluids into and out of the tank.

The thickness of the corrosion barrier

88

depends upon the particular capacity rating of the tank

14

. In the embodiment being described, the thickness of the corrosion barrier

88

is in the range of about 0.042 to about 0.100 inches, and preferably about 0.060 inches, including about two or three layers or windings of reinforcement material.

Alternatively, the corrosion barrier

88

could include a low surface energy fluorinated thermoplastic thin sheet liner such as a 5 to 10 mil (0.005 to 0.010 inches) thick polyvinylidene fluoride (PVDF) film which has a low permeability rate and is corrosion resistant to most chemicals. The low surface energy of PVDF is approximately 20 to 23 dynes per centimeter compared to stainless steel which is over 300 dynes per centimeter. The low surface energy of PVDF or other fluorinated thermoplastics prevent cargoes from sticking to the inner side wall of the tank thus allowing most cargoes to drain to the bottom of the tank for easy pumping and cleaning.

An inner wall

90

surrounds the corrosion barrier

88

. The inner wall

90

is formed from at least a resin material such as organic/inorganic polymers, flouro polymers, etc., and a reinforcement material such as fiberglass, aramid carbon fibers, graphite fibers, organic fibers, etc. The inner wall

90

provides structural integrity to the tank

70

. In the preferred embodiment, the resin material is an organic/inorganic polymer such as a siloxirane and the reinforcement material is fiberglass.

The thickness of the inner wall

90

depends upon the particular capacity rating of the tank

70

and the thickness of the other structural layers of the side wall

86

as described further below. In the embodiment being described, the thickness of the inner wall

90

is in the range of about 0.030 to about 0.100 inches, and preferably about 0.060 inches, including about four layers or windings of reinforcement material.

A first layer of energy absorption material

92

surrounds the inner wall

90

. The energy absorption material

92

can be formed from a honeycomb material, a high-density foam material, or a combination of honeycomb and high-density foam materials, etc. The use of honeycomb and/or high-density foam materials for the layer

92

results in a sandwiched sidewall construction that provides high strength with light weight. Further, the energy absorption material

92

absorbs energy at a constant rate. The energy absorption is due to the loading increasing up to a peak value (bare compressive strength) before starting to crush at a uniform load (about 50% of the peak load) until it bottoms out (can no longer crush).

The energy absorption property of the layer

92

protects against spillage in the event that the tank

70

were to be damaged. The tank

70

becomes oval or elliptical when a sufficient external load is present. This ellipticalization, along with the inherent energy absorption characteristics of at least the layer

92

, makes the composite cargo tank

70

almost unbreakable. In the preferred embodiment, the layer

92

is formed from a combination of honeycomb and high-density foam materials having a rating of 6 to 9 lbs/sq. ft. The honeycomb material can have any suitable cell construction such as rectangle, pentagram, quintuple, and preferably, sextuple or octagonal. The thickness of the layer

92

depends upon the desired level of structural integrity for the tank

70

. For instance, the thickness of the layer

92

is in the range of about 0.25 to about 0.50 inches, and preferably about 0.38 inches.

A middle wall

94

surrounds the layer of energy absorption material

92

. As with the inner wall

90

, the middle wall

94

is formed from at least a resin material such as organic/inorganic polymers, flouro polymers, etc., and a reinforcement material such as fiberglass, aramid carbon fibers, graphite fibers, organic fibers, etc. The middle wall

94

also provides structural integrity to the tank

70

. In the preferred embodiment, the resin material is an organic/inorganic polymer such as a siloxirane and the reinforcement material is fiberglass.

The thickness of the middle wall

94

depends upon the particular capacity rating of the tank

70

and the thickness of the other structural layers of the side wall

86

. In the embodiment being described, the thickness of the middle wall

94

is in the range of about 0.040 to about 0.150, and preferably about 0.080, including about five layers or windings of reinforcement material.

A second layer of energy absorption material

96

surrounds the middle wall

94

. As with the layer

92

, the layer

96

can also be formed from a honeycomb material, a high-density foam material, or a combination of honeycomb and high-density foam materials, etc. And, the use of honeycomb and/or high-density foam materials for the layer

96

results in a double sandwich sidewall construction that provides higher strength with lighter weight relative to the single sandwich sidewall construction of FIG.

7

. However, it should be appreciated that substantially the same strength to weight ratio of the sidewall

86

can be achieved by varying the performance characteristics of one or more of the layers that form the sidewall

52

, such that the thickness of one or more of the layers

56

-

60

, the material composition of the layers

56

-

60

, etc.

The energy absorption property of the layer

96

increases the protection against spillage in the event that the tank

70

were to be damaged. In the preferred embodiment, the layer

96

is formed from a rigid phenolic foam material having a density of approximately 6-9 lbs/sq. ft. The thickness of the layer

96

depends upon the desired level of structural integrity for the tank

70

. For instance, the thickness of the layer

96

is in the range of about 0.25 to about 0.100 inches, and preferably about 0.38 inches.

An outer wall

98

surrounds the layer

96

. The outer wall

98

is formed from at least a resin material such as organic/inorganic polymers, flouro polymers, etc., and a reinforcement material such as fiberglass, aramid carbon fibers, graphite fibers, organic fibers, etc. In the preferred embodiment, the resin material is a phenolic resin and the reinforcement material is fiberglass. The use of phenolic resin in the outer wall

98

not only contributes to the structural integrity of the tank

70

, but it also provides a fire resistance property to the tank

70

.

Fire protection of the triple wall (inner wall

90

, middle wall

94

and outer wall

98

) composite tank

70

can also be obtained by a number of other means, such as, but not limited to; 1) intumescent coatings which produce a ceramic-like insulating char at rapid temperature rises up to 2000° F. in five minutes, 2) fire retardant matrixes, 3) inorganic topcoat composites with steel mesh to dissipate localized heat or other such means, etc.

The thickness of the outer wall

98

depends upon the desired level of structural integrity and the desired level of fire resistance for the tank

70

. In the preferred embodiment, the thickness of the outer wall

98

is in the range of about 0.050 to about 0.250 inches, and preferably about 0.125 inches, including about nine layers or windings of reinforcement material.

A number of sensing or monitoring devices

100

such as stress gauges, load cells, liquid level gauges, temperature gauges, thermal couples, etc., can be embedded between any of the layers forming the side walls

86

of the storage tank

70

, preferably during manufacture, to monitor various tank and/or liquid cargo parameters. In the embodiment being described, the sensing devices

100

are mounted between the inner wall

56

and the first energy absorption layer

92

. The sensing devices can be coupled to external monitoring equipment (not shown) by wires or by telemetry antennas.

By incorporating stress gauges or load cells into the lower portion of the tank

70

, such as the central cylindrical portion

72

, the actual amount of cargo in the tank can be accurately monitored. That is, by knowing the empty weight of the composite storage tank, the loaded weight of the composite storage tank, and the specific gravity of the cargo in the composite storage tank, the actual amount of cargo can be determined in a known manner.

Fiber optic wires can also be embedded within the side walls

86

of the storage tank

70

, to allow for lighting within the tank. Video analysis of the inside of the tank increases safety for ship personnel by eliminating the need for a person to enter into a tank that could contain poisonous gases.

The invention has been described with reference to the preferred embodiment(s). Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

For instance, the composite storage tanks of the present invention can be placed onboard maritime vessels other than ocean-going ships, such as river barges, and other types of seaborne structures.

Further, the present invention contemplates the use of various other multi-layered side wall constructions for composite storage tanks incorporating additional or fewer structural layers, additional or fewer energy absorption layers, and additional or fewer corrosion barriers and/or fire resistance layers, etc. The side wall constructions shown in

FIGS. 7 and 9

are for purposes of illustration only and are not to be construed as limiting the present invention.

Number	Name	Date
3325037	Kohn et al.	Jun 1967
3502239	Worboys et al.	Mar 1970
3830180	Bolton	Aug 1974
3927788	Zinniger et al.	Dec 1975
4378403	Kotcharian	Mar 1983
5368184	Fay et al.	Nov 1994

Maritime chemical tanker having composite tanks for storing and/or transporting liquid organic and inorganic chemicals and the like

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